Single fill and use syringe

ABSTRACT

It is an object of the present invention to provide a syringe which is as cheap to manufacture as the standard plastic disposable syringe but which cannot conveniently be reused after it is filled and used once. 
     The syringe comprises a cylindrical barrel (2) and inside the barrel (2) a cylindrical plunger (9) with a resilient base (10) in sealing relation with the barrel (2), the plunger (9) having at least one circumferential groove (13a) and the barrel having an inwardly extending circumferential projection (11) around its aperture (8) such that the projection (11) engages the groove (13a) to prevent withdrawal of the plunger (9).

TECHNICAL FIELD

This invention relates to syringes and more particularly to medicalsyringes which can only be used once.

BACKGROUND ART

Medical syringes comprise a cylindrical barrel and a plunger with acylindrical base made of resilient material located in sealing relationwithin the barrel and a needle mounted at the base of and incommunication with the barrel.

Originally the barrel was made of glass and the syringe was designed formultiple use with either the needle or the whole syringe being subjectedto sterilisation between uses. However, for convenience and in order tominimize cross infection, the syringes most used in medicine now areplastic disposables.

Although relatively cheap and disposable, these syringes can be reusedand usually are by drug users amongst whom the spread of Acquired ImmuneDeficiency Syndrome (AIDS) is on the increase because of the sharing ofsyringes.

Many prior art syringes have been designed in an attempt to preventreuse. Some use complicated mechanisms to prevent withdrawal of theplunger; these are difficult to manufacture and greatly increase thecost over the plastic disposable. Others use techniques in which theplunger collapses or the seal between the plunger and the barrel isbroken, which prevents suction. None of these have proved to be reliableand affordable and although medically desirable have not beensuccessful.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a syringe which isas cheap to manufacture as the standard plastic disposable syringe butwhich cannot conveniently be reused after it is filled and used once.

This invention comprises a syringe having a cylindrical barrel andinside the barrel a cylindrical plunger with a resilient base in sealingrelation with the barrel, the plunger having at least onecircumferential groove and the barrel having an inwardly extendingcircumferential projection at its aperture such that the projectionengages the groove to prevent withdrawal of the plunger.

In a preferred form of the syringe of this invention the plunger has onegroove located so that engagement with the projection on the barreloccurs when the plunger is pressed home fully and a second groovelocated between the first groove and the base so that engagement withthe projection occurs before the plunger is pressed home fully.

BRIEF DESCRIPTION OF THE DRAWINGS

Following is a description of a preferred embodiment of the inventionwith reference to the drawings in which FIG. 1 is a perspective view ofa syringe with part of the barrel cut away.

BEST MODE FOR CARRYING OUT THE INVENTION

The syringe 1 consists of a barrel 2 having a needle assembly 3,including a non-removable needle 4 at its end 5. The other end 6 of thebarrel 2 has an oblong flange 7 serving as a finger support aroundaperture 8.

Extending through aperture 8 is a cylindrical plunger 9 with a base 10made of resilient material in air-tight relation with the inner barrelwall 2a such that withdrawal of the plunger 9 will result in the inwardsuction of liquid through the needle 4. Plunger 9 is provided with twoannular grooves 13a and 13b adjacent to its outer end and the inner wall2a of barrel 2 has an annular barb 11 located adjacent to its outerextremity. Plunger 9 is further provided at its outer end with a flange20 adapted to sit within a recess 7a of flange 7 when the base 10bottoms on end 5 of the barrel.

The syringe is supplied to the user with the plunger 9 partiallywithdrawn so that groove 13b is just outside the barrel 2. The userfills the syringe 1 by withdrawing the plunger 9 to the full extent ofthe barrel while the needle is inserted in the liquid to be injected.

The barrel has a portion 12a which is additional to the measured doseand greater than the travel of the plunger between grooves 13a 13b .This allows the full measured dose viz. 10 mls to be drawn into thesyringe without the groove 13b passing into engagement with the barb 11of the barrel.

The syringe is asperated by pushing the plunger 9 until the base 10 islevel with the dosage mark required and then the liquid injected bypushing the plunger home. After groove 13b passes barb 11 it will beimpossible to withdraw the plunger because of the locking engagement ofthe barb in the groove for the reverse direction of motion.

The barrel can be extended and the groove 13b can be located so thatthis engagement occurs when between 50% and 90% of the dose has beeninjected. Preferably, engagement occurs when 70% of the dose has beeninjected. Accordingly it is not possible to inject more than 70% of thedose and still reuse the syringe.

Further, when the plunger (9) is pushed home fully, the flange 20 sitswithin the recess 7a of flange 7. In this position it is difficult toobtain purchase on the plunger in an attempt to force withdrawal fromits locking engagement with the barrel.

I claim:
 1. A syringe (1) having a cylindrical barrel (2) and inside thebarrel (2) a cylindrical plunger (9) with a resilient base (10) insealing relation with the barrel (2), the plunger (9) having a firstcircumferential groove (13a) and designed to engage an inwardlyextending circumferential projection (11) disposed about the barrel (2)around its aperture (8) such that the first groove (13a) engages theprojection (11) to prevent withdrawal of the plunger (9) when base (10)bottoms on the end (5) of the barrel (2) and the plunger (a) having asecond groove (13b) designed to engage the projection (11) before theplunger (9) is pressed home and with the barrel having (2) a portion(12a) which is additional to a measured dose and greater than the travelof the plunger (9) between grooves (13a) and (13b).
 2. The syringe ofclaim 1 in which the travel of the plunger (9) between the grooves (13a)and (13b) is equivalent to 30% of the measured dose.